Require Python 3.6 for consider f-string check (#5024)

* Require Python 3.6 for consider f-string check

Co-authored-by: Ville Skyttä <ville.skytta@iki.fi>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

4 files changed, 35 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index 19aed403b..bb023b552 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -20,6 +20,11 @@ Release date: TBA
 ..
   Put bug fixes that should not wait for a new minor version here
 
+* Don't emit ``consider-using-f-string`` if ``py-version`` is set to Python < ``3.6``.
+  ``f-strings`` were added in Python ``3.6``
+
+  Closes #5019
+
 * Fix regression for ``unspecified-encoding`` with ``pathlib.Path.read_text()``
 
   Closes #5029
@@ -29,9 +34,6 @@ What's New in Pylint 2.11.1?
 ============================
 Release date: 2021-09-16
 
-..
-  Put bug fixes that should not wait for a new minor version here
-
 * ``unspecified-encoding`` now checks the encoding of ``pathlib.Path()`` correctly
 
   Closes #5017
diff --git a/pylint/checkers/refactoring/recommendation_checker.py b/pylint/checkers/refactoring/recommendation_checker.py
index 84c399988..b22f18acd 100644
--- a/pylint/checkers/refactoring/recommendation_checker.py
+++ b/pylint/checkers/refactoring/recommendation_checker.py
@@ -7,6 +7,7 @@ from astroid import nodes
 
 from pylint import checkers, interfaces
 from pylint.checkers import utils
+from pylint.utils.utils import get_global_option
 
 
 class RecommendationChecker(checkers.BaseChecker):
@@ -56,10 +57,15 @@ class RecommendationChecker(checkers.BaseChecker):
             "Formatting a regular string which could be a f-string",
             "consider-using-f-string",
             "Used when we detect a string that is being formatted with format() or % "
-            "which could potentially be a f-string. The use of f-strings is preferred.",
+            "which could potentially be a f-string. The use of f-strings is preferred. "
+            "Requires Python 3.6",
         ),
     }
 
+    def open(self) -> None:
+        py_version = get_global_option(self, "py-version")
+        self._py36_plus = py_version >= (3, 6)
+
     @staticmethod
     def _is_builtin(node, function):
         inferred = utils.safe_infer(node)
@@ -321,10 +327,12 @@ class RecommendationChecker(checkers.BaseChecker):
 
     @utils.check_messages("consider-using-f-string")
     def visit_const(self, node: nodes.Const) -> None:
-        if node.pytype() == "builtins.str" and not isinstance(
-            node.parent, nodes.JoinedStr
-        ):
-            self._detect_replacable_format_call(node)
+        if self._py36_plus:
+            # f-strings require Python 3.6
+            if node.pytype() == "builtins.str" and not isinstance(
+                node.parent, nodes.JoinedStr
+            ):
+                self._detect_replacable_format_call(node)
 
     def _detect_replacable_format_call(self, node: nodes.Const) -> None:
         """Check whether a string is used in a call to format() or '%' and whether it
diff --git a/tests/functional/p/py_version/py_version_35.py b/tests/functional/p/py_version/py_version_35.py
new file mode 100644
index 000000000..ee880c54a
--- /dev/null
+++ b/tests/functional/p/py_version/py_version_35.py
@@ -0,0 +1,14 @@
+"""Test warnings aren't emitted for features that require Python > 3.5"""
+# pylint: disable=invalid-name
+
+# consider-using-f-string -> requires Python 3.6
+"Hello {}".format("World")
+
+
+# ------
+# CodeStyle extension
+
+# consider-using-assignment-expr -> requires Python 3.8
+a1 = 2
+if a1:
+    ...
diff --git a/tests/functional/p/py_version/py_version_35.rc b/tests/functional/p/py_version/py_version_35.rc
new file mode 100644
index 000000000..6f19ec36a
--- /dev/null
+++ b/tests/functional/p/py_version/py_version_35.rc
@@ -0,0 +1,3 @@
+[MASTER]
+load-plugins=pylint.extensions.code_style
+py-version=3.5